Study: Low snow years increasing

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Predicting how much snow will fall at Lake Tahoe is a long-held pastime of skiers, professional weather watchers, resort operators and barstool meteorologists alike.

And the safe bet for precipitation pundits in coming years may be the under, according to a recently published study looking at the likelihood of high and low snowfall seasons on a warming planet.

"What's new about this study is we're looking at the occurrence of extremes," said Noah Diffenbaugh, a researcher at Stanford University and the lead author on the study published in the November edition of Nature Climate Change.

Climate models used in the study show an "imminent shift towards low snow years in the Northern Hemisphere."

"Our results suggest that many snow-dependent regions of the Northern Hemisphere are likely to experience increasing stress from low snow years within the next three decades, and from extreme changes in snow-dominated water resources if global warming exceeds 2 C above the pre-industrial baseline," according to the study.

The research also found the frequency of low snow years is expected to intensify in most snow-dominated areas of North America, western Eurasia and southeastern Eurasia during the 21st Century. More than 80 percent of the years between 2070 and 2099 in those regions are expected to have low snowfall, according to the study.

More years with less snow will have wide-ranging implications for both natural and man-made systems.

Diffenbaugh noted the critical importance of snowpack to water supply in the Western Hemisphere. A higher frequency of low snow years is expected to lead to decreased availability of snow for recreation, increased wildfires, more die-off in forest ecosystems and decreased water supply for agriculture, energy, consumption and river ecosystems, according to the study.

"The occurrence of extremely low snow years becomes widespread by the late twenty-first century, as do the occurrences of extremely high early-season snowmelt and runoff (implying increasing flood risk), and extremely low late-season snowmelt and runoff (implying increasing water stress)," the study finds.

Early season snowmelt has been highlighted in several recent State of the Lake Reports by UC Davis, which also note a higher likelihood for precipitation to fall as rain rather than snow in the Lake Tahoe region.

"The average minimum air temperature now exceeds the freezing temperature of water, which points to more rain and less snow, as well as earlier snowmelt," according to the 2012 State of the Lake report.

"Snow has declined as a fraction of total precipitation, from an average of 52 percent in 1910 to 36 percent in present times," the report continues. "In Tahoe City, snow represented 50 percent of 2011 total precipitation, much higher than the long-term trend."

Complex topography of the snow dominated mountain regions do present some complications for models used in the study led by Diffenbaugh.

Higher resolution studies looking at more specific geographic locations, such as the Sierra Nevada, are underway, Diffenbaugh said.